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1 /*

3 *

4 * @APPLE_LICENSE_HEADER_START@

5 *

6 * This file contains Original Code and/or Modifications of Original Code

7 * as defined in and that are subject to the Apple Public Source License

8 * Version 2.0 (the 'License'). You may not use this file except in

9 * compliance with the License. Please obtain a copy of the License at

10 * http://www.opensource.apple.com/apsl/ and read it before using this

11 * file.

12 *

13 * The Original Code and all software distributed under the License are

14 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER

15 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,

16 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,

17 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.

18 * Please see the License for the specific language governing rights and

19 * limitations under the License.

20 *

21 * @APPLE_LICENSE_HEADER_END@

22 */

24 #include <machine/cpu_capabilities.h>

25 #include <architecture/i386/asm_help.h>

26 #include <mach/i386/syscall_sw.h>

28 .text

30 /* Subroutine to make a preempt syscall. Called when we notice %ebx is

31 * nonzero after returning from a PFZ subroutine. Not in PFZ.

32 *

33 * All registers preserved (but does clear the %ebx preemption flag).

34 */

35 .align 2

36 .private_extern _preempt

37 .globl _preempt

38 _preempt:

39 pushq %rax

40 pushq %rcx

41 pushq %r11

42 movl $(SYSCALL_CONSTRUCT_MACH(58)),%eax /* 58 = pfz_exit */

43 xorl %ebx,%ebx

44 syscall

45 popq %r11

46 popq %rcx

47 popq %rax

48 ret

50 /* Subroutine to back off if we cannot get the spinlock. Called

51 * after a few attempts inline in the PFZ subroutines. This code is

52 * not in the PFZ.

53 * %rdi = ptr to queue head structure

54 * %ebx = preemption flag (nonzero if preemption pending)

55 * Uses: %rax.

56 */

57 .align 2

58 .private_extern _backoff

59 .globl _backoff

60 _backoff:

61 testl %ebx,%ebx // does kernel want to preempt us?

62 jz 1f // no

63 call _preempt

64 1:

65 pause // SMT-friendly backoff

66 cmpl $0,16(%rdi) // sniff the lockword

67 jnz 1b // loop if still taken

68 ret // lockword is free, so reenter PFZ